The brake actuators used in heavy vehicles (bus, lorries, trucks, trailers, etc.) are divided into two groups; one of which is the spring brake actuators and the other is the service brake chambers.
Service brake chambers are used if the vehicle is desired to be stopped or slowed down and functions when the foot brake is actuated.
Compressed air which comes from compressor when the foot brake is actuated by driver, fills pressure chamber between diaphragm and pressure housing. The diaphragm; moves in an upward direction by means of this compressed air, pushes the shaft and enables the braking force, which is transferred to the wheels of the vehicle.
If the vehicle is desired to be fixed or in the case that there is an air leakage in the air system, the emergency chamber of the spring brake actuators brakes and provides fixing the vehicle.
Service chamber of the spring brake actuators are used if the vehicle is desired to be stopped or slowed down and functions when the foot brake is actuated as the service brake chambers.
In the known state of the art, service brake chamber mainly comprises, a pressure housing, a non-pressure housing, diaphragm, shaft and return spring. Air inlet connections are welded onto these parts and all parts are painted and coated to prevent corrosion.
In the known state of the art, pressure housing and non-pressure housing parts of the service brake chambers are produced by means of cold forming such as deep drawing of steel sheet. Connection process between pressure housing and non-pressure housing is performed by fixing with clamp ring and clamp ring bolt after placing and compressing the diaphragm between pressure housing and non-pressure housing by press machine. Sealing is provided, because diaphragm is compressed between pressure housing and non-pressure housing, and this connection is secured by a clamp ring.
Unlike the connection method using clamp ring in the prior art, there are various connection methods like roll-form method which one of the skin of the pressure or non-pressure housing, is bended over the other one, or connection methods using connection rings.
Another service brake chamber involved in the known state of the art is an invention according to the TR 2008 04238 B numbered patent document. In this invention, plastic pressure housing and flange group, and a steel non-pressure housing, are used. The connection between the pressure and non-pressure housing is carried out by bending skirt of the steel non-pressure housing onto the plastic pressure housing.
The service brake chambers which are made of steel sheet (pressure housing, non-pressure housing, flange, etc.) are exposed to corrosion because of atmospheric effects. In the known state of the art, service brake chambers which are made of steel, are coated by protective paintings or coatings to prevent corrosion. But an failure caused by the coating and painting may lead to the untimely damage of the service brake chamber which is of vital importance for heavy commercial vehicles.
In addition, no burrs are required onto the pressure and non-pressure housing parts, to enable service brake chambers operate efficiently and safety. Single burr onto the pressure and non-pressure housing parts even may adversely affect the operation of the chamber. Particularly, during the connection between pressure housing, non-pressure housing and diaphragm, it is very important to be burr-free connecting surfaces. For this reason this parts must be suitable for connection by means of second or third operations (punching, machining etc.) after main deep drawing operation which the parts are produced. This additional processes may lead to additional labor and production costs.
Furthermore, when differences of dimensional measurements and tolerances arising from the pressure and non-pressure housings which are made by steel sheet, press cutting, pressing, machining, stoning, welding, painting and coating etc. operations in the known state of the art, also be added; situation which parts are discarded to scrap, occurs due to different dimensional measurements and tolerances of the parts from values should be, before assembly.
Another technical problem in the known state of the art is connecting the air connection ports on the pressure housing by welding operation. Burr and sealing problems may occur due to mistakes of the welding operations. Sealing has critical importance, because the pressure housing is the part that air pressure which activates the diaphragm, is given.
However, the weigh disadvantage arising from the weight of the steel sheet used in the service brake chambers which are made by steel sheet. The reduction of the weight of the automotive parts in the automotive industry, has a great importance especially in terms of security and low fuel consumption. Service brake chambers have weight disadvantage in the design, vibration and connection fields. Unfortunately, weight factor is not taken into account so much in designing and development processes of the service brake chambers produced in the known state of the art.
In order to overcome the technical problems described above, pressure housing and flange are made of plastic, non-pressure housing is made of steel sheet in the invention described in TR 2008 04238 B numbered application in the known state of the art. In this invention, the connection between the pressure and non-pressure housing is carried out by bending skirt of the steel non-pressure housing onto the plastic pressure housing. Although the important advantages provided by this invention, technical problems are not fully resolved because breakage or deformation may occur on the plastic housing part during the bending skirt of the steel non-pressure housing onto the plastic pressure housing. This deformation and damage, may leads to sealing problem or completely damage of the service brake chamber.
It is necessary to compress the diaphragm between pressure and non-pressure housing by means of applying force, for providing the sealing during the connection between pressure and non-pressure housing of the service brake chambers. There is a possibility of deformation of the plastic part during this connection operation when one of the pressure or non-pressure housing is made by steel and the other one is made by plastic because steel part is harder than plastic part. This is another technical disadvantage of this invention.
In the applications where both pressure housing and non-pressure housing are plastic, metal clamp may give damage the plastic pressure housing and non-pressure housing during the compression of the parts in the case where the connection is provided by a steel clamp.